Estuaries are valuable ecosystems that are easily affected by human activities within the watershed. One determinant of water quality for in an estuary is the presence of suspended sediments. The use of satellite sensors to remotely sense visible and near-infrared reflectance allows for suspended particulate matter (SPM) and suspended particulate inorganic matter (SPIM) concentrations to be monitored on a repetitive synoptic scale. Previously presented algorithms for relating remote sensing reflectance (Rrs) and SPM/SPIM concentrations were evaluated for the Weeks Bay estuary in Alabama. Additionally, numerous potential SPM/SPIM concentration retrieval algorithms using the Landsat-8 satellite were determined through regression analysis, as well as through the consideration of the inherent optical properties of the water body. The most robust empirical algorithm produced an RMSE of 12.50% and utilized the band combination of Ln(Band4)/Ln(Band3), while the most robust semi-analytical algorithm produced an RMSE of 16.34% and utilized the band combination of Band4/Band3.

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Sea level rise and changing storm frequency and intensity resulting from climate change create tremendous amounts of uncertainty for coastal species. Intertidal species may be especially affected since they are dependent on daily inundation and exposure. The eastern oyster Crassostrea virginica is an economically and biologically important sessile intertidal species ranging from Canada to the Gulf of Mexico. Declines and changes in distribution of oyster populations has forced commercial harvesting to spread from subtidal to intertidal reefs. We investigated the potential responses of intertidal C. virginica to sea level rise, and the response of larval settlement to sedimentation which is likely to increase with higher water levels and storm frequency. Inundation was used as a proxy for sea level rise. We hypothesized four possible outcomes for intertidal oyster reefs as a result of changes in inundation due to sea level rise: (a) intertidal reefs become subtidal and remain in place, (b) intertidal reefs will be lost, (c) intertidal reefs migrate shoreward upslope and remain intertidal, and (d) intertidal reefs will grow in elevation and remain intertidal. To test the plausibility of these four outcomes, oyster ladders were placed at two sites within Apalachicola Bay, Florida, USA. Ladders supported oyster recruitment mats at five heights within the range of intertidal elevations. The bottom-most mat was placed near mean low tide, and the top mat near mean high tide to investigate the effect of tidal inundation time on C. virginica. Sediment traps were attached to ladders with openings at equal elevation to the oyster mats. Ladders were deployed for one year starting in June 2012, and again in June 2013, during peak oyster recruitment season. Monthly for six months during year one, sediment was collected from traps, dried to constant weight and weighed to obtain a monthly average for total sediment at each elevation. At the end of one year, oyster mats were collected from the field and examined for the following responses: live oyster density, mean oyster shell length of live oysters, mean oyster shell angle of growth relative to the benthos, and mean number of sessile competitors. We used AICc to identify the most plausible models using elevation, site, and year as independent variables. Oyster density peaked at intermediate inundation at both sites (maximum 1740 oysters per m2), it decreased slightly at the mean low tide, and sharply at the mean high tide. This response varied between years and sites. Mean oyster shell length peaked near mean low tide (6.7 cm), and decreased with increasing elevation. It varied between years and sites. Oyster shell angle of growth relative to the benthos showed a quadratic response for elevation; site but not year affected this response. Sessile competitor density also showed a quadratic response for elevation and varied between sites and years. Barnacles were the primary spatial competitor reaching densities of up to 28,328 barnacles per m2. Total monthly sedimentation peaked at the lowest elevations, and varied by site, with an order of magnitude difference between sites. Sediment increased with decreasing elevation. Outcomes a, c, and d were found to be viable results of sea level rise, ruling out complete loss of intertidal reefs. Outcome (a) would be associated with decrease in oyster density and increase in oyster length. Outcome (c) would require the laying of oyster cultch upslope and shoreward of current intertidal reefs, as well as the removal of any hard armoring or development. Outcome (d) remained possible, but is the least likely requiring a balance between sedimentation, oyster angle of growth, and recruitment. This should be further investigated. A laboratory experiment was designed to test relative impact of varying sediment grain sizes on settlement of C. virginica larvae. Previous studies showed that suspended solids resulted in decreased larval settlement when using mixed sediment grain sizes. Predicted storm levels and hurricane levels of total suspended solids were used in flow tanks. Sediment from the field experiment was sieved into seven size classes, the most common five of which were used in the experiment since they represented 98.8% of total mass. Flow tanks were designed and built that held 12 aged oyster shells, instant ocean saltwater, and sediment. Oyster larvae were added to the flow tanks and allowed one hour to settle on shells. Each run utilized one of the five size classes of sediment at either a high or low concentration. Following the one-hour settlement period, oyster shells were removed from the flow tank and settled larvae were counted under a dissecting microscope. Settlement was standardized by settlement area using Image J. AICc model selection was performed and the selected model included only grain size, but not concentration. A Tukey's post hoc test differentiated < 63 µm from 500 – 2000 µm, with the < 63 µm grain size having a negative effect on oyster larval settlement. This indicates that the smaller grain sizes of suspended solids are more detrimental to oyster larval settlement than larger grain sizes. The oyster ladder experiment will help resource managers predict and plan for oyster reef migration by cultch laying, and or associated changes in oyster density and shell length if shoreward reef growth is not allowed to occur. The laboratory experiment will help to predict the impacts of future storms on oyster larval recruitment. Together this information can help managers conserve as much remaining oyster habitat as possible by predicting future impacts of climate change on oysters.

Coastal ecosystems continue to face numerous negative impacts from human activities ranging from local nutrient enrichment to global warming. These threats have complex effects on coastal biogeochemistry, which in turn alters ecosystem ecology and climate. While sediments have long been recognized as cornerstones of marine ecosystem functioning, the impacts of anthropogenic change on benthic biogeochemical cycling remain challenging to constrain. This knowledge gap stems from technological issues as measuring marine sediment processes under natural conditions is a formidable challenge. To help move the field of sediment biogeochemistry forward, I developed a novel mass spectrometer-based system and used it to quantify dissolved gas fluxes from marine sediments. In Chapter One, I survey the field of underwater mass spectrometry from its inception three decades ago to the present. Through comprehensive descriptions of the current status of the technology, field applications to date, and future trends, I provided guidance for how to leverage this powerful new tool to measure gaseous compounds in the under sampled ocean. In Chapter Two, I review the role of permeable shelf sediments in marine nitrogen cycling. My synthesis of the small but growing body of work on nitrogen cycling in shelf sands exposed conflicting evidence surrounding the nitrogen removal capacity of permeable sediments, and I proposed targeted approaches, such as the development of noninvasive in situ technologies, to resolve these controversies. In Chapter Three, I present a newly developed flow-injection sampling system that can be coupled to a mass spectrometer to measure a range of dissolved gas species in the pore water of highly permeable sandy sediments. Rigorous calibration and validation experiments demonstrate that this novel system can quantify dissolved gas depth profiles, as well as fluxes across the sediment-water interface, in permeable sediments. Furthermore, with my prescribed design improvements, this tool promises to provide in situ data in dynamic sandy environments. In Chapter Four, I used the flow-injection mass spectrometer system to measure benthic fluxes of gaseous nitrogen and methane from cohesive sediments subjected to low oxygen conditions and varying organic matter loads. The unprecedented high temporal resolution of the gas flux data revealed the complex and dynamic effects of changing environmental conditions on the capacity of sediments to remove reactive nitrogen and regulate methane emissions. / 2024-11-08T00:00:00Z

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Salt marshes are important habitats that provide many ecosystem services, but they are susceptible to the impacts of sea level rise (SLR), often resulting in emergent vegetation loss. In areas with enough sediment input, marshes can keep pace with SLR by gaining elevation or through upland migration. However, salt marshes in areas with limited sediment input, such as the Grand Bay National Estuarine Research Reserve, often cannot keep pace with sea level rise. Additionally, the rate of SLR is increasing making it more difficult for marshes to keep pace. To assess the short-term response of marsh vegetation to sea level rise, percent cover, stem density, and elevation, data from 2016 to 2020 in four different marsh elevation zones were analyzed in this study. Results demonstrated that the four marsh elevation zones are responding disparately to SLR. These findings indicate that it is imperative to implement restoration plans to account for site variability to conserve these vital habitats.

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